1. Field of the Invention
This invention relates to filters for liquids, and more particularly to filtering devices intended to withstand appreciable pressures and for use with corrosive liquids such as plating baths and the like.
2. Description of the Related Art Including Information Disclosed Under 37 CFR .sctn..sctn.1.97-1.99
U.S. Pat. No. 1,632,960 discloses a liquid filter wherein the inlet and outlet fittings are carried by a casing and do not interfere with removal and replacement of filter elements that are mounted on a removable head. However, the entire set of elements when clogged must be removed as a unit and such elements, being hung, are susceptible to damage and require compressive strength in the form of a built-in support or structure means whereby their fabrication is costly. Moreover, limitations exist as to the size and extent of filtering that the disclosed elements are capable of. The design does not lend itself to immersion of the lower portion of the filter in a bath, if this should be found desirable.
U.S. Pat. No. 2,083,005 shows a top-replacement filter device wherein a collapsible basket element has an inner spring to counteract the force of the incoming liquid. As the sediment builds up, the basket element is under continuing pressure and loses its effectiveness, as well as being susceptible to collapse.
U.S. Pat. No. 4,187,179 discloses filter elements which include elongate perforated structural members, but the filtering portions of the same are not adequately supported to withstand appreciable loading and can bulge outward, malfunction and fail when overloaded.
U.S. Pat. No. 4,402,828 discloses a plastic filter intended for use with acid liquids, wherein inlet and outlet connections can remain undisturbed during filter replacement, and wherein non-rigid filter sleeves are supported by rigid perforated inner tubes and are capable of replacement from the top of the casing. However, for such replacement obviously the entire casing, sealed at its bottom by O-rings, must be removed in order to unfasten and pull off the clogged filter sleeves, and replace them.
U.S. Pat. No. 4,552,661 discloses a filter with fixed inlet and outlet fittings and an openable cap for removal of filter bags which collect residue internally and are liable to rupture when overloaded, as well as to interfere with one another if they bulge outward. Access to the casing interior for cleaning purposes is restricted, and the arrangement does not lend itself readily to immersion in a bath, where such an installation might be desirable. Limitations exist, as well, as to the thickness of the walls of the bags and the costs of fabrication of the same.
U.S. Pat. No. 4,455,227 discloses a heat-exchange filter device wherein all of the filter elements are carried by the top cover plate and removable as a unit, as distinguished from filter elements which can be removed individually. This makes for a cumbersome replacement procedure, which is undesirable when dealing with the corrosive or acid liquid baths. The device is obviously not suitable or intended for immersion in a liquid bath.
U.S. Pat. No. 4,517,086 shows a filter device wherein the outlet fitting must be disconnected prior to opening of the casing and replacement of the filter element.
U.S. Pat. No. 4,526,689 shows a strainer device wherein individual rigid baskets fit into sockets in a top plate. However, the baskets are not tightly sealed to the top plate, nor are there bottom-mounted supports for the baskets, rigidly carried by the bottom plate of the casing.